1. Field of the Invention
The present invention relates to the treatment of vascular disorders and in particular to treatment of blood vessels by using local energy emitting devices and conveying means.
2. Invention Disclosure Statement
The blood vessels are the part of the circulatory system that transport blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart, the capillaries, which enable the actual exchange of water and other substances between the blood and the tissues; and the veins, which carry blood from the capillaries back towards the heart.
The human venous system of the lower limbs consists essentially of the superficial venous system and the deep venous system, both connected by perforating veins. The superficial system comprises the great and the small saphenous veins, while the deep venous system includes the anterior and posterior tibial veins, which converge to form the popliteal vein near the knee. The popliteal vein, in turn, becomes the femoral vein when joined by the small saphenous vein.
The venous system comprises valves, whose main function is to achieve unidirectional blood flow back to the heart. Venous valves are usually bicuspid valves, with each cusp forming a blood reservoir, which force their free surfaces together under retrograde blood pressure. As a consequence, when properly operating, retrograde blood flow is prevented, allowing only antegrade flow to the heart. Thus, under normal conditions venous flow is unidirectional, thanks to correct functioning of the endothelial flaps that oppose reflux. When a valve is absent or becomes incompetent their cusps are unable to seal properly under retrograde pressure gradient, so retrograde blood flow occurs. When retrograde blood flow occurs, pressure increases in the lower venous sections, dilating veins and usually leading to additional valvular failure.
Valve failure, usually referred to as venous insufficiency, is a chronic disease that can lead to skin discoloration, varicose veins, pain, swelling and ulcerations. Varicose veins refer to blood vessels that have become enlarged and twisted and have progressively lost their wall elasticity. Due to the widening of the blood vessels, vein valves cannot be completely closed and veins lose their ability to carry blood back to the heart. This leads to an accumulation of blood inside the vessels, enlarging and twisting the veins even more.
Various methods can be used to eliminate the problem of insufficient veins, including, sclerotherapy, surgery (vein stripping), electro-cautery, and laser treatments. Prior art methods and devices are intended to obliterating and/or eliminating the insufficient veins. This forces the blood to flow through the remaining healthy veins. As a consequence, venous function is not restored in insufficient veins. Instead, these veins are either extracted or closed in order to prevent blood from circulating through them, thus avoiding reflux. The treated veins are no longer capable of conveying blood and generally are no longer present. As a consequence, vein is lost for potential use in future cardiac and other by-pass procedures. Furthermore, recurrence or persistence of varicose veins may occur, particularly if the valvular problem is not resolved. These techniques present another important limitation. They are effective (possible) only for treating superficial veins. They are not indicated for veins at 5 or more cm deep.
Patients with deep venous insufficiency (DVI) must be treated by surgical methods after failure of non-surgical methods. Venous valve reconstruction is a recognized option for treatment of DVI. The concept of remodeling of altered anatomical geometry is applied in a surgical technique called annuplasty, which aims to reduce the circumference of dilated valve rings, thus restoring their shape and function. This concept is accepted for the restoration of valvular defects, cardiac as well as venovascular defects. The restoration techniques of annular dilation, aim to restore the diameter of the circumference by means of internal reduction, thus seeking to achieve proper valve closure and therefore unidirectional valve flow.
Open surgery is one way to repair diseased vessel valves. But it is a costly and risky treatment, and it does not always achieve desired results. Most patients prefer not to undergo such treatment after evaluating cost-benefits.
With the objective of carrying out vascular treatment by restoring venous function of insufficient veins, some approaches have been developed. These techniques are directed towards restoring venous function by making the valve competent.
Two main techniques for restoring venous functionality have been used: implanting a replacement venous valve; and directly treating venous valve incompetence.
In the first case, a valve is implanted inside the vein in order to replace insufficient valve. In general terms, implanted valve can be artificial (made from non-organic materials), a xenograft (from animals) or an autogenous graft (extracted from other site of patient's body). For instance, in U.S. Pat. No. 6,299,637, Shaolian et al. disclose a self-expandable venous valve implant. It comprises a pivotable leaflet and a tubular wire support. Leaflet is positioned in the flow path, for permitting flow in a forward direction and resisting flow in a reverse direction.
In another example, disclosed by Gomez-Jorge et al. in WO00047136A1, a vascular valve prosthesis is formed by suturing a vein valve segment (for example, from a bovine jugular vein) which has been trimmed in order to reduce its thickness.
Venous valve implants present disadvantages. Frequently, and especially in artificial prosthesis, implanted valves require an increased opening pressure. As a consequence, patient condition may further deteriorate, instead of improving. In addition, these surgical treatments require skillful and meticulous techniques, and often patients require multiple interventions. Furthermore, the use of compression stockings is often required even after surgical intervention to ensure relief of symptoms and durability of the operation. Moreover, implant rejection as well as thrombosis may occur in these procedures. Also, procedure is more invasive, more time consuming and its outcome is not as predictable as vein obliteration. Therefore, cost-effectiveness becomes an important drawback.
In the second case, valve competence is intended to be restored by different means. For example, WO09638090A1 discloses an attempt to restore valve competence by reducing insufficient vein diameter. Vein lumen is constricted using an extravascular corrector attached to vein in the region of the incompetent valve. Corrector is made from a resilient shape-memory alloy in order to adapt to vein's structure. This technique is an invasive procedure and presents some drawbacks. Since a foreign body is placed inside organism, there are risks of infection and implant may be encapsulated or even rejected. In addition, material mechanical properties may be altered in time due to biological degradation.
In another approach, described in U.S. Pat. No. 6,322,559 by Daulton et al., vein diameter is also reduced just below an incompetent venous valve, by using a RF heating catheter that constricts the collagen layer. This catheter uses a low-voltage radiofrequency generator to heat expandable electrodes placed on catheter's tip (expandable coil). The surgical procedure consists in a percutaneous insertion of an introducer into the saphenous vein just below the level of the knee, under ultrasound guidance. The electrodes are then expanded to contact the vein wall and heated, during a treatment period of a few minutes. This approach presents some disadvantages. First, it is usually carried out under general or spinal anesthesia, with all the associated risks and complications. Second, since the risk of thrombosis is believed to be substantial with this treatment, low-molecular weight (LMW) heparin is given subcutaneously before and after the procedure, during approximately a week, thus requiring professional attention over this time span. Third, it is a rather long procedure and recurrence is observed after one year, as vein is dilated almost to pre-treatment diameter. Finally, due to catheter's small diameter, it is only appropriate for small veins. If a larger catheter was used, greater veins could be treated, but size of catheter would make it too cumbersome to manipulate.
In order to restore venous function, the controlled shrinkage and strengthening of the vein structure needs to be accomplished. This in turn cannot be accomplished well and in a reliable manner by the relatively unspecific application of RF energy. RF treatment is limited to the reduction of vein diameter near the valve, hoping that consequently, valve will start working properly again, thus preventing reflux. However, if weakened valve is not treated and therefore still present, recurrence may occur.
In an alternative approach, U.S. Patent Publication 2006/0189967A1 by Masotti et al. describes a treatment of varicose veins by means of the recovery of the tone of the venous wall, using a pulsed holmium laser. This is disclosed to be accomplished by causing a hyalinizing sclerosis in the extracellular matrix of the median coat, but preserving tunica intima from thermal damage, using wavelengths between 800 and 2900 nm, preferably 2100 nm (holmium laser). This wavelength is proposed as it is characterized by a high absorption coefficient in water and a low absorption coefficient in hemoglobin. Nevertheless, experience has shown that wavelengths around this value are highly absorbed in blood (probably due to its high content of water), so it is unlikely that radiation would cause its major effect on the tunica media since absorption inside vein lumen will be high. In addition, pulsed holmium lasers usually emit radiation in narrow pulses. Thus, in order to achieve appropriate energy levels for producing certain effects on tissue, laser power must be high. High power radiation applied in short bursts usually creates undesired shockwaves, which in turn will produce undesired and unpredictable effects on tissue. It is well known by those skilled in the art that holmium lasers may not be recommendable for applications in which precise amounts of energy are to be applied and non-linear processes must be avoided. This patent also claims a wavelength range of 800-2900 nm, but effects produced in biological tissues due to the different wavelengths comprised in this range are substantially different. Therefore, it is unlikely that the desired described effect would be achieved with all the wavelengths in the claimed range. For instance, a wavelength of 800 nm is highly absorbed in hemoglobin, thus it is improbable that laser radiation reaches the tunica media without affecting tunica intima.
Size and cost are also important issues to take into account when using holmium lasers. Diode lasers, for example, have numerous advantages over ionic crystal lasers. Among them, are higher output, at reduced dimensions and weight. They also have simpler and smaller air cooling systems. Moreover, being integrated with optical fibers, they have a high reliability and do not need alignment.
Effective and convenient treatment of deep and superficial venous insufficiency due to venous valve incompetence remains elusive. There is thus a need for a minimally invasive vascular treatment that improves on the state of the art, providing a safe and precise vessel function restoration, to recover vessel function. The present invention addresses these needs.